With the development of software and semiconductor technology and data processing technology, information devices are gradually becoming smaller, so that the importance of inputting characters using such information devices is gradually increasing.
Meanwhile, the input of various characters or instructions to such information devices exhibits many problems.
For example, input devices, such as keyboards, used in Personal Computers (PCs) or notebook computers, cause difficulty when realizing small-sized information devices because there is a limitation on the reduction in the size thereof, and touch screen schemes used in Personal Data Assistants (PDAs) and keypad schemes used in mobile phones are inconvenient because the speed of input is slow and the incidence of erroneous input is high.
In order to input letters, numbers or symbols to the above-described information devices, such as PCs, notebook computers, PDAs or mobile phones, at a higher speed, it is necessary to perform a so-called one action-one phoneme input, in which one phoneme (character) is input through one input action.
When such one action-one phoneme input is applied to the Korean alphabet, it is necessary to provide buttons or input keys for inputting 24 or more characters on an information device.
When the target language of input is English, Japanese or some other language, a larger number of buttons or input keys is required than in the case of the Korean alphabet.
However, conventional input devices used in various types of information devices adopt a scheme of assigning characters to respective input keys and inputting the characters by striking or pressing the input keys using the fingers.
Due thereto, it is difficult to arrange 24 or more finger-sized input keys on a personal mobile information terminal having a small area for the arrangement of input keys, such as a mobile phone. This is the reason why it has been difficult to realize small-sized keyboards to date.
In particular, in the case of mobile phones, since 24 or more Korean alphabet letters are input using only 12 buttons, it is inevitable that a plurality of letters is arranged on each button.
Accordingly, a repeated input phenomenon, in which an input action is repeated twice or three times to input one letter (phoneme), occurs frequently, so that input time increases in proportion to the number of repetitions and erroneous input occurs frequently.
Further, since such an input method itself is greatly complicated, there is a problem in that it takes a long time to become accustomed to the input method.
In order to overcome the above problem, in the case of the input of the Korean alphabet, a character input method of inputting characters through combination, known as Cheonjiin, has been proposed.
This method is advantageous in that, since a desired character is generated by combining fundamental letters with each other, the number of input buttons to which characters are assigned can be reduced, but is disadvantageous in that, since an input button must be repeatedly pressed until desired letters are combined, input time increases in proportion to the number of repetitions.
Furthermore, technologies, including a roll-up keyboard, which can be rolled up and then carried, and a virtual laser keyboard, which is configured to project an image of a keyboard onto a surface, detect the locations of the fingers when actions similar to keyboard input actions are performed on the image using the fingers, and perform input, have been proposed.
However, such types of input devices have problems in that they are inconvenient because they must always be carried, and in that the types of input devices are not suitable for application to personal portable information terminals requiring input in the state in which the personal portable information terminals are held in the hands while moving because input can be performed only in the state in which those types of input devices are placed on supporting surfaces.